Until now, practitioners of chemical hair straightening arts have been unable to successfully increase and maintain negatively-charged cation receptive sites in alkali-straightened (relaxed) hair to simultaneously strengthen and restore its textural quality to that substantially resembling hair in relatively good condition.
Most commonly used relaxers are based on hydroxide-containing alkalis, sulfites or thioglycolates. Of these, the most effective and popular are alkaline straightener compositions that produce stable lanthionine linkages in the hair. These chemical hair straighteners usually contain relatively strong alkalis, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide and guanidine hydroxide. The highly alkaline conditions (pH 12 to 14) of these products, however, causes a substantial amount of swelling in human hair. Consequently, some hydrolysis of the polypeptide chains in the hair protein at about pH 12.5 is inevitable.
Prolonged or unnecessary exposure of hair to a strong alkali weakens, breaks and even dissolves the hair. Thus, it is an accepted practice to minimize the time that the hair is exposed to highly alkaline hair straighteners. Towards this end, substantially all the straightener is immediately rinsed from the hair as soon as the desired partial or complete straightening effect is achieved. Further, to remove any residual hair straightener remaining in the rinsed hair, and to deswell the hair, an acidic neutralizer is applied immediately thereafter to the rinsed alkali-treated hair. Generally this acidic neutralizer is a nonalkaline shampoo or an acid rinse having a pH below 7, usually in a pH range between about 1 to about 6 and preferably close to the isoelectric region of human hair, approximately pH 4.
Some success in preventing further alkali attack on the hair is achieved by deswelling the hair in the foregoing manner. However, the textural quality of acid-treated hair is harsh and strawlike, unless known conditioners are included in the shampoo or rinse. The term "conditioners" refers to cosmetically useful emollients, such as oils, quaternary ammonium salts, cationic polymers and the like, known to those skilled in hair conditioning art.
It is known that human hair is negatively charged, i.e., more anionic, above its isoelectric region, and hence, more receptive to adsorbing cationic materials. There is also some indication that the cationic qualities of certain quaternary ammonium salts are enhanced under alkaline conditions. Finkelstein, et al., "The Mechanism of Conditioning of Hair with Alkyl Quaternary Ammonium Compounds," App. Polym. Symp., 18, 673 (1971), for example, report that the cationic properties of stearyltrimethyl ammonium chloride are greater at pH 7.5 than at pH 4.5. However, any attempt to enhance or sustain the cation-receptivity of alkali-straightened hair by further exposing it immediately to a non-acidic composition having a pH greater than 7 is generally avoided.
Thus, the non-polymeric quaternary ammonium salts often used for hair conditioning are employed at relatively low pH values rather than at higher pH values. Under alkaline conditions, such compounds tend to deposit an unacceptable delustering coating on the hair. Also, because of their relatively small molecular size, they are easily removed from the hair so conditioning benefits obtained are temporary.
As a result, cationic polymers, especially those containing quaternary nitrogen atoms, are more often used in hair conditioning compositions, because these polymers are usually substantive to hair at acidic pH values. The term "substantive" cannot be defined by distinctive physicochemical properties, but involves mechanisms such as adsorption, ion exchange and chemical interaction. As used herein, the term "substantive" or its grammatical variant "substantivity" refers to the retention of a cationic material deposited or adsorbed on the hair through several shampoo applications.
Not all cationic polymers, however, are alkali-compatible or stable under alkaline conditions. Some cationic polymers must first be complexed with some anionically active component already present on the hair or in the neutralizing shampoo to form a conditioning reaction product.
Proteinaceous materials that are water-soluble and substantive to hair are also known desirable compounds. A number of water-soluble hydrolyzed protein compounds are commercially available, some of which display cationic qualities under acidic conditions. However, their utility under alkaline conditions is limited, because they become neutral or anionic in character and some degradation of the amide groups in the protein portion takes place. Consequently, their use in non-acidic compositions is generally avoided.
Prior attempts have been limited, therefore, to applying conditioners under acidic or neutral conditions to at least improve the tactile feel, if not the strength of the alkali-straightened hair.
In one approach, a non-alkaline composition containing one or more of the foregoing conditioners is applied to the hair before the hair straightener. However, one drawback of this approach is that any conditioning benefit achieved generally does not survive the subsequent highly alkaline chemical straightening procedure. In addition, these conditioners may weaken the strength of the hair straightener product or interfere with its effectiveness.
This drawback was partially overcome by including a quaternary nitrogen-containing cationic polymer in the alkaline hair straightener product as described in U.S. Pat. No. 4,175,572. Such a product is presently marketed. However, the residual alkalinity in the hair following use of this product is substantially immediately neutralized by application of a non-alkaline neutralizing shampoo.
In another approach, a conditioning nonalkaline shampoo neutralizer is employed immediately after rinsing the straightener from the hair with water. However, a shampoo, by the manner in which it must be used, contacts the hair too briefly to maximize adsorption of cationic materials. Further, alkali-weakened hair may not withstand the manipulative actions inherently required for the shampooing process so some hair loss or breakage can occur.
U.S. Pat. No. 4,602,648 (hereafter the '648 patent) discloses the use of hydrolyzed proteins and/or cationic polymers in a "pre-shampoo normalizer" so-called because it is applied between the straightening step and the shampooing step. Several products following such a procedure are presently being marketed. However, the effectiveness of such normalizer compositions suffers the same drawbacks of prior acidic compositions.
The pre-shampoo normalizers of the '648 patent are acidic or nonalkaline compositions that are adjusted by the addition of acid to a pH of between 2.5 and 7. Thus, these compositions decrease, rather than increase, cation-receptive negatively-charged sites in the hair as the acidity of the composition neutralizes the alkaline residue in the hair. Thus, this approach constitutes, in effect, an acidic neutralization procedure, because the '648 patent normalizer step is followed by a shampooing step to remove both residual straightener and residual normalizer composition from the hair.
The '648 patent purports to take advantage of the sensitive state of the hair at a relatively high alkaline pH of between about 9 and 11 after the straightener treatment to mediate damage and improve the aesthetic qualities of the straightened hair. However, we have found from experience that when the method of this patent is followed, substantive conditioning and strengthening are not simultaneously achieved. This was determined by measuring the strength and subjective textural qualities of the straightened hair.
There is a need for a relatively simple method and a product that simultaneously strengthen and enhance the cation-receptivity of hair undergoing or about to undergo a highly alkaline hair straightening procedure. We have now surprisingly found that the cation-receptivity of alkali-straightened hair can be enhanced and sustained, while the hair is simultaneously strengthened, by applying the non-acidic compositions of this invention to hair in a post-straightening and pre-straightening step. The hair straightening method and texturing strengthener compositions of this invention satisfy that need.